In the prior art, to ensure service continuity of user equipment (UE), mobility management needs to be performed on the UE. For example, when moving from a coverage area of a source cell to a coverage area of a target cell, the UE needs to complete a handover between cells in a timely manner.
However, in an existing communications system, a design idea for mobility management is a design idea that UE follows a network (UE follows network). Using UE in an activated state as an example, to perform mobility management on the UE, each cell in a network sends a downlink reference signal for measurement performed by the UE. The UE reports a measurement result to a network side in a form of a measurement report, the network determines handover based on the measurement report from the UE, and the UE is handed over to a cell having a good signal condition, for data transmission.
However, in a subsequent evolution process of a mobile communications system, to meet a requirement on a huge amount of data communication, massive small cells (small cell) may be deployed in a hotspot area in a centralized manner. In this case, if the design idea that UE follows a network continues to be used, a problem that mobility management on UE is difficult is caused. For example, in a hotspot area, UE needs to measure massive small cells; this raises a relatively high requirement on a measurement capability of the UE. For another example, UE can be handed over only after performing measurement and reporting a measurement report, and due to a small coverage area of a small cell, the UE may quickly move out of the coverage area of the small cell. As a result, a handover may fail because the handover is not performed in a timely manner, for example, sending the measurement report to the small cell fails or sending a handover command fails. For still another example, because ultra dense cell deployment is performed, operations such as reporting a measurement report and performing a handover may cause massive air interface signaling, consuming massive air interface resources and massive network processing resources.